The invention relates generally to a device for measuring torsional moment on a shaft and, more particularly, to a torsion measuring device in which magnetic field detection devices generate a signal indicative of torsional moment.
French Patent No. 2,626,368A describes a device in which the angular shift of two magnetic field generators placed respectively in two perpendicular cross sections of a shaft is detected by two sensors with an all-or-nothing signal output and in which the torsional moment is proportional to the magnetic phase shift of the induction fields detected respectively by the sensors.
French Patent No. 2,661,246A describes a device in which the angular shift of two magnetic field generators is detected by a sensor with a signal output proportional to the torsional moment of the rotating shaft.
When the magnetic field generators consist of multipolar magnets, the sensitivity of the measurement of the torsional moment of such measuring devices is limited by the minimum length of manufacturing for magnets. This measurement is difficult to implement when the torsional moment is low and the drive moment is high.
A torsion measuring device applied to a steering column shaft of a motor vehicle should satisfy the following requirements:
measurement range .+-.10 m.N; PA1 sensitivity of the measurement .+-.0.1 m.N; PA1 maximum moment to be transmitted 200 m.N; PA1 maximum authorized angular shift between the input and the output of the measurement devices 4.degree.; and PA1 output electrical signal .+-.2 V around the value of the signal with a moment of zero and for any value of the moment in the measurement range.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.